Wacko Jacko rigged up an alarm to warn him if anyone approached his bedroom as he slept with kids, a new report said yesterday.

Former Los Angeles Police Detective Bill Dworin, who led the Michael Jackson child-sex probe 10 years ago, told Britain’s Sun newspaper he found the device installed at the star’s Neverland Ranch.

“To me it suggested it was a warning, in case something was occurring that was improper, that the activity would stop,” the ex-cop said.

Dworin was convinced in 1993 that he had enough evidence to charge Jacko, now 44, with molesting a schoolboy of 13 – but the Gloved One escaped any possible charges after forking over $20 million to the boy’s family in an out-of-court payoff.